Traditional "zero pressure" pallet accumulation conveyors (PAC) have utilized mechanical sensors and actuators. In one mode, as a product moves into a zone of these conveyors, a mechanical sensor is triggered. The sensor is linked to a mechanical actuator. The actuator then reacts with a clutch mechanism of the zone to either enable or disable the zone's movement. Using this concept, conveyor motors typically run continuously and the conveyor is often noisy due to the mechanical actuation of the zone. Where mechanical setups have not been either feasible or desirable, electrical sensors and actuators have been used. These devices have typically been connected to an external programmable logic controller (PLC). Software is then implemented that allows the PLC to control the conveyor in a similar fashion. Using these concepts results in unusually long setup times for either adjustment and/or wiring.
One example of an accumulation conveyor is disclosed in U.S. Pat. No. 5,042,644 to Davis. This patent discloses a zero pressure accumulation conveyor using a trigger assembly for the accumulation control. The trigger assembly is positioned along the conveyor run and is coupled to cam follower arms and valve bodies. Depression of the trigger assembly depresses the valve body, allowing air to pass from an air supply to a brake assembly cylinder. The brake assembly cylinder then restrains a torque tube thus isolating the driving force imparted by the drive shaft to the conveyor rollers.
U.S. Pat. No. 5,060,785 to Garrity discloses a control arrangement for an accumulating conveyer having a plurality of zones, each zone including an electrically-powered sensor. A logic circuit is associated with each sensor, the logic circuit comprising a first input, a second input from the sensor of its zone, a first output which sends a signal to the activator for that zone and a second output to send a signal to the input for the next zone. A circuit for each electronic sensor communicates with the circuit before and after itself to control the system. In this system, electronic sensors are used to indicate the presence of an article in a given zone. When the electric sensor senses an article blocking the sensing path, the signal interacts with the logic circuit to control the operation of the accumulation conveyor.
Accumulation conveyors using mechanical sensors and actuators are not without their disadvantages. First, in any system, the actuator reacts with a clutch mechanism of the zone to either enable or disable the conveyor's movement in that zone. Using this system, the conveyor motors typically run continuously. Moreover, the conveyor is often noisy due to the mechanical actuation of the zone.
While these mechanical systems have been replaced with electrical systems such as that disclosed in the Garrity patent, these electrical systems are not without their disadvantages either. The electrical systems containing logic circuits take an unusually long time for setup due to adjustments and/or wiring.
In light of the disadvantages noted above, a need has developed to provide accumulation conveyor controls which overcome the prior art's disadvantages. In response to this need, the present invention provides an accumulation conveyor control which eliminates both mechanical control such as trigger mechanisms, pneumatic systems, and logic circuit control devices.